Geologic units in Elko county, Nevada

Unit is present in all counties. Some counties divided the alluvium into younger and older units, and some did not. For those that did not, or used other generalized terms for Quaternary rocks, the unit Qal has been used for the general undivided alluvium. Additionally, when polygons have been edited and changed to alluvium, Qal was used as the general value; hence it now is present in all counties. Qya-Younger alluvium: Map unit is used in Churchill, Elko, Esmeralda, Eureka, Humboldt, Lander, and Lincoln Counties where geologic information suggests better-defined younger versus older alluvium. It is mostly interchangeable with Qal, except that it implies some specifically younger Quaternary deposits.

Tuffaceous and other young Tertiary sedimentary rocks. Most of these rocks are sedimentary with a strong volcanic component - a few are tuffaceous with a strong sedimentary component. This unit includes rocks originally mapped as the High Rock sequence in Washoe County; the Horse Camp Formation in northern Nye County; the Esmeralda Formation in Mineral and Esmeralda Counties; older lake beds in Lincoln County; the Belted Range Tuff; the Indian Trail Formation (now abandoned); Timber Mountain, Paintbrush, and Crater Flat Tuffs; Wahmonie and Salyer Formations in southern Nye County; the Siebert Tuff in Esmeralda County; the Muddy Creek Formation in Clark County; and the Thousand Creek and Virgin Valley “beds” in Humboldt County; and other unnamed units. It corresponds to units Ts3 and Tts from the 1978 State map. It is present in all counties.

Rhyolitic flows, domes, plugs, breccias, quartz latite, rhyodacite, quartz porphyry dikes, and other shallow intrusive rocks. This unit includes rocks mapped as the Cañon Rhyolite on the Washoe North map, the Jarbidge Rhyolite and phenorhyolitic and phenodacitic flows and domes on the Elko County map, and other unnamed units. It has a distribution similar to Tt3, with exposures in the northern and southern parts of the State, but only crops out in a few places in the central region. It corresponds to unit Tr3 on the 1978 State map, and also includes a few rocks mapped as Trt on the 1978 State map. This unit is exposed in every county except White Pine.

Basalt flows, cinder and lava cones, gravel, and tuffaceous sedimentary rocks mostly in Elko and some in Humboldt Counties. This unit includes the Banbury Formation (Stewart and Carlson, 1978) and the Big Island Formation in Elko County and other unnamed units. It corresponds to unit Tbg from the 1978 State map.

Includes units mapped as the High Rock sequence on the Washoe North map; the Timber Mountain, Paintbrush, Crater Flat, and Belted Range Tuffs, and Indian Trail Formation (now abandoned) on the Nye South map; the Thirsty Canyon Tuff on the Nye South and Esmeralda maps; and other unnamed units. Locally it includes tuffaceous sedimentary rocks interstratified with tuffs. It is present in the northernmost part and southernmost parts of the State, and is not exposed in the central region. It corresponds to unit Tt3 on the 1978 State map, although a few rocks also mapped as Trt on the 1978 State map also are included. It is present in Clark, Churchill, Washoe, Nye, Lincoln, Lyon, Douglas, Carson, Esmeralda, Elko, Humboldt, Pershing, and Mineral Counties.

These Permian rocks include cherty limestone, dolomite, shale, sandstone, bioclastic limestone, and phosphatic limestone exposed in Elko, White Pine, Lincoln, and Clark counties. This unit includes rocks mapped as the Phosphoria Formation; the Gerster Limestone, Plympton Formation, Kaibab Limestone, and Grandeur Formation of the Park City Group; the Park City Group undivided; the Toroweap Formation; and the Coconino Sandstone. Unit Pc is disconformably overlain by Triassic unit TRmt in scattered places in eastern and southern Nevada. It depositionally overlies unit Psc. It matches closely with unit Pc of Stewart and Carlson (1978).

(Lower Permian, Leonardian and Wolfcampian)at surface, covers 2 % of this area

This largely siliciclastic unit of siltstone, sandstone, limestone, and dolomite crops out in Elko, White Pine, Lincoln, and Clark Counties. It includes rocks originally mapped as the Arcturus Formation, Rib Hill Sandstone, undivided Kaibab Limestone, Toroweap Formation, and Coconino Sandstone in Clark County; and the Pequop Formation and red beds in Lincoln County. Unit Psc represents a strong influx of clastic material over the carbonate shelf during the Early Permian, presumably derived primarily from the craton to the east. It is depositionally overlain by unit Pc and lies conformably above unit PIPc. At its western and northern edges it can be difficult to distinguish from Permian clastic rocks of the Siliciclastic overlap assemblage (units Pacl and PIPacl). It follows closely with unit Psc of Stewart and Carlson (1978).

Includes the Valmy Formation in Eureka, Humboldt, Lander, and Pershing Counties; Devonian to Upper Cambrian mudstone, shale, chert, siltstone, and gray quartzite in Elko County (Leslie, Isaacson, and others, 1991); Devonian to Ordovician slate, chert, limestone, and sandstone in Mineral County; Devonian to Upper Cambrian rocks in Eureka County (Finney, Perry, and others, 1993); some rocks originally mapped as the Palmetto Formation in Esmeralda County (Albers and Stewart, 1972; Ferguson and Cathcart, 1954); and the Sonoma Range Formation (Ferguson, Muller, and Roberts, 1951) in the Sonoma Range in Humboldt County (later included with the Valmy Formation). The distinctions between these rocks and rocks of the Slope assemblage (DOts) are (1) a more complex and varied history of deformation; (2) less well-defined internal stratigraphic characteristics, which may be a function of structural complexity; (3) fewer shale, siltstone, and sandstone interbeds; (4) less carbonate; and (5) in the Roberts Mountains at least, the Ordovician rocks of this unit are older than the Slope assemblage Ordovician rocks. Like unit DOts, no basement is preserved with these rocks, making it difficult to determine where they were originally laid down, and how far they have been transported. This unit includes Devonian, Silurian, Ordovician, and uppermost Cambrian rocks imbricately faulted and folded together. In a few places, Silurian rocks are defined regionally and broken out separately (Ss), but for the most part they are included in this unit. Likewise, significant exposures of Devonian rocks have been included in unit MDst, but many more are not differentiated from this unit. A great variety of depositional settings are present in ocean basins, and this diversity is represented in these rocks (Watkins and Browne, 1989). While these rocks share a common deformation history indicative of east-directed transport from folding and thrusting along regional structures in different areas of Nevada, these rocks have been subject to additional distinct tectonic events during the Mesozoic and the Paleozoic resulting in significant spatial variability in the structure of these rocks (Evans and Theodore, 1978; Oldow, 1984b).

(Middle Pennsylvanian to Lower Mississippian)at surface, covers 2 % of this area

Unit crops out across all of eastern Nevada, generally east of 116 west longitude, and somewhat farther west in the southern half of the State. It includes rocks mapped as the Chainman Shale in Elko, northern Nye, and Lincoln Counties; the Diamond Peak Formation in northern Nye, Elko, Eureka, and White Pine Counties; the Scotty Wash Quartzite in Lincoln County; the upper part of the Eleana Formation in Nye County; and undivided sedimentary rocks in Eureka and Lincoln Counties. Clastic and carbonate rocks mapped in Elko County, including undivided Moleen and Tomera Formations (the Tomera Formation includes Middle Pennsylvanian rocks) are also grouped here. Most of these rocks are Upper Mississippian and Lower Pennsylvanian in age, but unit IPMcl also includes Lower Mississippian rocks, overlapping with unit MDcl where they have not been clearly distinguished. In places the Chainman Shale is time transgressive into the Diamond Peak Formation, and in other places they represent different coeval facies, based on limited biostratigraphic data. Where possible, younger siliciclastic rocks have been separated from the older sequence that includes the Pilot Shale and Joana Limestone because of significant differences in the character of the rocks. Unit IPMcl is overlain conformably or disconformably in the eastern part of its exposure by carbonate rocks of units PIPc and (or) IPMbc. In the northern and western parts of its exposure it is overlain unconformably by Permian and Upper Pennsylvanian clastic rocks of the Siliciclastic overlap assemblage (Pacl or PIPacl). Assignment of siliciclastic Pennsylvanian units to either unit IPMcl or the unconformably overlying PIPacl is challenging unless biostratigraphic data are available and outcrop observations reveal the presence of the unconformity such as in Carlin Canyon (Dott, 1955). Unit IPMcl lies either conformably or disconformably above unit MDcl.

Unit includes andesite or dacite flows, flow breccias, and hypabyssal rocks in Lander County, andesitic to latitic flows, pyroclastic rocks, and phenoandesitic and phenolatitic flows in Elko County, and other undifferentiated volcanic rocks in other counties. Present in Humboldt, northern Nye, Churchill, Elko, Eureka, Lander, and White Pine Counties. It corresponds to the 1978 State map unit Ta1.

(lower Oligocene to Upper Cretaceous (?))at surface, covers 1 % of this area

Includes the Sheep Pass Formation and equivalents in northern Nye, Lincoln, Elko, Eureka, Lander, and White Pine Counties. In most places the Sheep Pass Formation is Paleocene or Eocene (Fouch, Hanley, and Forester, 1979), although rocks from the Carlin-Piñon Range area that contain Late Cretaceous fossils have been included in the Sheep Pass Formation (Smith and Ketner, 1976, 1978). It corresponds to unit Ts1 on the 1978 State map.

Calcareous shale, siltstone, sandstone, chert, quartzite, and greenstone in the Vinini Formation in Lander, Eureka, Elko, and northern Nye Counties, and the Clipper Canyon Group in the northern Toquima Range are the core rocks of unit DOts. Difficulties in identifying distinct paleogeographic settings within Ordovician slope facies rocks are discussed in Finney and Perry (1991) and Finney and others (1993). On a regional scale, the distinction between this unit and rocks traditionally mapped as the Valmy Formation (DCs) is the preponderance of shale and siltstone of cratonal derivation that is present in the Vinini rocks but less common in the Valmy rocks. Both rock units contain bedded chert, massive quartzite, and greenstone (Finney and Perry, 1991) in many places. Many lower Paleozoic rocks grouped here likely formed in a basinal rather than slope setting, but the presence of more common siliciclastic horizons of shale, siltstone, and sandstone distinguish them as a regional grouping from the lower Paleozoic Basin assemblage rocks. Whether this is a function of distinct paleogeographic settings of coeval units as interpreted by early workers, or is actually an age distinction of older (Valmy) versus younger (Vinini) Ordovician rocks, as suggested more recently for at least the Roberts Mountains (Finney, Perry, and others, 1993), remains to be determined on a regional scale. Originally thought to be primarily Ordovician, studies and biostratigraphic data have demonstrated that this unit consists of tightly imbricated Devonian, Silurian, and Ordovician rocks (Coles and Snyder, 1985; Noble and Finney, 1999). The distinction between units DOts and DCs as currently mapped on a regional scale is ambiguous in many places. Identifying the numerous occurrences of Devonian and Silurian rocks that are embedded within this unit on a regional scale would significantly enhance our understanding of the complex structural history of these rocks. These rocks are everywhere in structural contact with other Paleozoic rocks including units IPMcl, Pacl, Dc, MDst, DSt, DSc, and Dcd. Stratigraphic correlation has been made between rocks of the Vinini Formation and the Carbonate shelf sequence in Nevada (Finney and Perry, 1991) on the basis of occurrence of quartzite that is coeval with the shelf unit Ocq. While this does suggest a connection between the Ordovician rocks of this composite unit and North America, the quartzite was deposited along a 1,000-mile length of the margin (Ketner, 1986) and thus does not constrain the rocks of unit DOts to deposition along a specific section of the margin. These rocks are unconformably overlain sporadically by units Pacl and PIPacl, and post-Paleozoic cover rocks.

Unit consists mostly of older alluvium and alluvial fans. It also includes various stream deposits, gravel, fanglomerates, and older gravels. It is not very consistent in description from county to county. This is used in all counties except Clark.

Unit is mixed on the Washoe North map with basalt, tuff, diatomite, and tuffaceous sediments. It includes the units mapped as Qls from the 1978 State map. It is present in Churchill, Washoe, Nye, Esmeralda, Elko, Eureka, Humboldt, Lander, Lincoln, Mineral, and Pershing Counties.

The Golconda terrane is composed of deformed and imbricated thrust slices of upper Paleozoic rocks including deep-marine, pelagic and turbiditic, carbonate, terrigenous clastic and volcaniclastic rocks, radiolarian chert and argillite, and pillow basalt (Silberling, Jones, and others, 1992). While the terrane is characterized by a great diversity of rock types, all rocks are strongly deformed with an east-vergent fabric, a distinguishing characteristic of this terrane (Brueckner and Snyder, 1985; Jones, 1991a; Miller, Kanter, and others, 1982; Murchey, 1990; Stewart, Murchey, and others, 1986). It crops out in a long sinuous belt, up to 100 mi wide in places. Southwest of Mina, the belt trends east from the California border to just north of Tonopah, and then bends north-south to the west of Longitude 117° to about 50 mi north of Winnemucca, where it bends again, sharply to the east-north of Tuscarora with significant exposures eastward and to the northern border of the State. Outcrops of the Golconda terrane are present in Mineral, Esmeralda, northern Nye, Churchill, Elko, Humboldt, Lander, and Pershing Counties. It includes some rocks originally mapped as Banner and Nelson Formations in Elko County; rocks originally mapped as the Excelsior Formation in Mineral and Esmeralda Counties, later assigned to the Black Dyke and Mina Formations by Speed (1977b); the original Havallah and Pumpernickel Formations (Muller, Ferguson, and Roberts, 1951; Roberts, 1964; Silberling and Roberts, 1962), later revised to structural sequences (Murchey, 1990; Stewart, MacMillan, and others, 1977; Stewart, Murchey, and others, 1986; Theodore, 1991; 1994) in Elko, Humboldt, Lander, and Pershing Counties; the Inskip Formation in Pershing County; the Mitchell Creek Formation in Elko County; the Pablo Formation in northern Nye County; and the Schoonover Formation (see unit GChr) in Elko County. In all of the places where rocks of the Golconda terrane were originally believed to form a stratigraphic sequence, detailed mapping and biostratigraphic analysis with radiolarians and conodonts has demonstrated that it is characterized by complex imbrications of rocks ranging from mid-Permian through latest Devonian age (Holdsworth, 1986; Jones, 1991b; Miller, Holdsworth, and others, 1984; Murchey, 1990; Stewart, MacMillan, and others, 1977). In Pershing County, the Golconda terrane is unconformably overlain by Triassic volcanic rocks of the Koipato Group (TRkv) which form the stratigraphic base to the Humboldt assemblage (TRc, JTRs). In Mineral and Esmeralda Counties, it is unconformably overlain by the Gold Range assemblage (JTRgor) of mainly nonmarine, terrigenous clastic, and volcanogenic Upper Triassic and younger rocks. Elsewhere in northern and southwestern Nevada, it is structurally overlain by Mesozoic accreted terranes. Across the length of its exposure from the Independence Mountains north of Elko to the Candelaria region south of Mina, the base of the Golconda terrane has a remarkably consistent structural emplacement relationship with adjacent rocks. It commonly lies on a low-angle structure above Permian and Pennsylvanian rocks of the Siliciclastic overlap assemblage. In places where these rocks are missing, it is faulted directly onto either the nearby lower Paleozoic Basin assemblage, the Nolan belt rocks, or the Harmony Formation of the Dutch Flat terrane. The type locality of this regional feature, the Golconda thrust is well exposed along Interstate Highway 80 at Edna Mountain near the town of Golconda (Ferguson, Roberts, and Muller, 1952), and in the open pits of mines near Battle Mountain (Theodore, T., oral commun., 2006). In southwestern Nevada, the lower Lower Triassic rocks of the Candelaria Formation overlie Permian and Pennsylvanian Siliciclastic overlap assemblage rocks, and the Golconda terrane is exposed nearby, but not observable directly on top of the Candelaria because of younger cover rocks. Elsewhere, there is no youngest age constraint for the age of emplacement. In several places, notably in the Osgood Mountains and the Toiyabe Range, it is also bounded by large, steeply dipping, mélange-like shear zones against older rocks of the Nolan belt. Stratigraphic and structural studies within the terrane have locally identified lithostratigraphic groupings (Erickson and Marsh, 1974a, b; Jones, 1991a; Murchey, 1990), but only the Home Ranch subterrane can presently be distinguished on a regional scale (GChr). Interpretations of the size and character of the late Paleozoic basin where these rocks formed and the nature of its Late Permian or Early Triassic accretion are as varied as the lithologic and structural characteristics of the terrane itself (see references above).

Andesite flows and breccias and other related rocks of intermediate composition such as dacite, rhyodacite, quartz latite, and biotite-hornblende porphyries. This unit includes units mapped as the South Willow Formation on the Washoe North map, the Milltown Andesite on the Nye South and Esmeralda County maps, the Mizpah Trachyte on the Nye North map, and other units. It corresponds to unit Ta2 on the 1978 State map. It crops out in all counties except Clark, Eureka, Lyon, Douglas, and Carson.

(Lower Permian and Pennsylvanian)at surface, covers 0.8 % of this area

Present in Elko, White Pine, Lincoln, and Clark Counties. This unit represents mostly Upper Pennsylvanian and Lower Permian rocks that have not otherwise been separated into units Psc or IPMbc. Unit includes unnamed Pennsylvanian and Lower Permian limestone and sandstone beds in Lincoln County, the Bird Spring Formation in Clark County, the Riepe Spring and Ely Limestones (undivided) in White Pine County, and limestone and dolomite rocks not otherwise assigned in Elko County. This unit lies depositionally below unit Psc and above the Ely Limestone (IPMbc) where it is mapped separately. Where unit IPMbc is not mapped separately in southern Nevada, the unit lies directly on Mississippian carbonate (Mc) and in White Pine County it rests on undivided Chainman and Pilot Shales and Joana Limestone (shown as either unit IPMcl or MDcl).

Welded and nonwelded silicic ash flow tuffs. Aside from alluvium, this unit covers more of Nevada than any other rock, with over 4,000 polygons representing it on this map. It is principally exposed in the central regions of the State. It locally includes thin units of air fall tuff and sedimentary rocks. It includes rocks mapped on the Washoe South, Lyon, Douglas, and Carson Counties maps as the Hartford Hill Rhyolite Tuff (now abandoned); on the Nye South map as the tuff of White Blotch Spring, the tuffs of Antelope Springs, and the tuff of Monotony Valley; in Lander County it is mapped as the Bates Mountain Tuff, Caetano Tuff, Edwards Creek Tuff, New Pass Tuff, tuff of Hall Creek, and the tuff of McCoy Mine; in Lander and Pershing Counties it is the Fish Creek Mountains Tuff; on both of the Nye County maps it is the Fraction Tuff; it also includes the Pancake Summit Tuff, Northumberland Tuff, Shingle Pass Tuff, some outcrops of Darrough Felsite shown to be Tertiary (other outcrops have been shown to be Mesozoic or Paleozoic), tuffs of Moores station, tuffs of Peavine Canyon, tuffs of the Pancake caldera complex, the Stone Cabin Formation, tuff of Saulsbury Wash, tuff of Kiln Canyon, the Tonopah Formation, tuffs of Hannapah, tuff of Bald Mountain, the Needles Range Formation, and the Calloway Well Formation on the Nye North map; in Esmeralda County it is the Kendall Tuff and latite; and in northern Nye and Lander Counties it is the Toiyabe Quartz Latite (now abandoned), and other unnamed units. It corresponds to unit Tt2 on the 1978 State map. It crops out in every county except Clark.

(lower Oligocene to middle Eocene)at surface, covers 0.8 % of this area

Includes rhyolitic lava of Portuguese Mountain in northern Nye County, rhyodacite in Elko Hills in Elko County, and other unnamed units. The rhyodacite in Elko Hills was shown on the 1978 State map as unit Tr1, and on the Elko County map as the Jurassic Frenchie Creek Rhyolite. It was subsequently renamed the Rhyodacite of Elko Mountain (Ketner, 1990) when the late Eocene radiometric age of approximately 39.5 Ma was obtained. It corresponds to unit Tr1 on the 1978 State map. This unit is present in northern Nye, Elko, Eureka, and White Pine Counties.

Granodiorite, granite, and related rocks make up the largest group of granitic intrusions exposed in Nevada. They are present in every county, and are especially abundant in west-central Nevada in an arcuate belt along the border with California extending north and eastward towards Idaho.

Concentrated in two areas of the State; common in the west-central part of the State along the California border in Mineral, Esmeralda, Lyon, Douglas, and Carson Counties. There is another more widely scattered group in eastern and central Nevada in Elko, Eureka, and White Pine Counties. Scattered occurrences also are present in Humboldt, Churchill, Lander, and Pershing Counties. Compositions are mainly granitic, granodiorite, and quartz monzonite.

(Oligocene, Cretaceous, and Jurassic with Paleozoic, Proterozoic, and Archean protolith)at surface, covers 0.7 % of this area

In the Ruby Mountains and East Humboldt Range in Elko County, this unit is an orthogneiss with amphibolite and paragneiss. It includes granodiorite and quartz monzonite gneiss, granitic to dioritic gneiss, biotite and muscovite schist, quartzitic schist, quartzite, calc-silicate rocks, marble, migmatitic Oligocene granodiorite, and Cretaceous and Jurassic granite. The protoliths for the East Humboldt Range orthogneiss include Archean through Paleozoic rocks (Lush, McGrew, and others, 1988; McGrew, Peters, and Wright, 2000).

Includes generally cliff-forming, thin- to thick-bedded limestone. These rocks are mainly shallow water subtidal, intertidal, and supratidal deposits formed on a broad inner carbonate shelf (Stewart, 1980). The Devils Gate Limestone and Guilmette Formation in northern Nevada are the principal units, and the Sultan Limestone is included from the southern part of the State. Unit is overlain (usually disconformably) by the Pilot Shale of unit MDcl except in southernmost Nevada where it is overlain by Mississippian carbonate (Mc). It depositionally overlies Middle and Lower Devonian unit Dcd. In a few places, such as southern Nevada and parts of Eureka County, regional mapping did not distinguish the Upper and Middle Devonian section from the Lower Devonian section, and all of the Devonian is included in unit Dc. Rocks mapped as the Simonson Dolomite would fit into this depositional sequence (sequences 9 and 10 of Cook and Corboy, 2004), but they are not differentiated from the underlying dolomites in White Pine or Elko Counties, so they are all included in unit Dcd here, not unit Dc. This unit crops out in Clark, Elko, Eureka, Lander, Lincoln, Nye, and White Pine Counties.

Unit is used for pre-Lake Lahontan deposits, weakly consolidated gravel and sand, older gravels, pediment gravels, and gravel deposits. It includes all units designated as QToa on the 1978 State map. This unit is used in all counties.

(Middle Ordovician to Upper Cambrian)at surface, covers 0.6 % of this area

Carbonate platform rocks are present in Nye, Lincoln, Elko, Eureka, Lander, White Pine, Esmeralda, and Clark Counties. This unit is primarily Ordovician in age but does include Upper Cambrian rocks at the base (Page, Lundstrom, and others, 2005). The Pogonip Group, including the Antelope Valley Limestone is the most common name used. In Clark County it also includes the Ely Springs Dolomite, and includes the Eureka Quartzite in White Pine and Clark Counties. Unit OCc corresponds to depositional sequence 2 of Cook and Corboy (2004). Where Ocq is mapped separately, it overlies OCc. Otherwise OCc is depositional under SOc, or in southern Nye and Clark Counties, it is overlain directly by DSc where SOc is not differentiated. Unit OCc depositionally overlies unit Cc.

(Permian to Middle Pennsylvanian)at surface, covers 0.6 % of this area

Unit represents rocks that are stratigraphic sequences that include both Lower Permian and Pennsylvanian rocks, and also sections that have not been broken out regionally into younger and older Permian and Pennsylvanian units. The Antler sequence (Roberts, 1964) rocks are present in Humboldt and Lander Counties and include the Antler Peak Limestone, the Highway Limestone, the Battle Formation or Battle Conglomerate, and the Etchart Limestone. The Brock Canyon Formation of Permian or Pennsylvanian age is in the Cortez Mountains in Eureka County and the siliciclastic and carbonate Strathearn Formation is exposed in Elko County (Theodore, Moring, and others, 2003). Scattered remnants of conglomerate, sandstone, siltstone, and limestone in Nye County, and unnamed limestone and dolomite in Elko County are also included. In the northern Hot Creek Range in Nye County, PIPacl is faulted with lower Paleozoic Carbonate shelf sequence rocks. Additionally, Early Triassic fossils in the area have caused reassignment of some of the rocks to the Candelaria Formation (TRcl). In the Pancake Range, PIPacl lies on the Ely Limestone (IPMbc). In the Toquima Range, the Pennsylvanian Wildcat Peak Formation lies unconformably on Slope assemblage rocks (DOts). In the Monitor Range and in Lander County, this unit lies unconformably on the lower Paleozoic Basin assemblage rocks (DCs). At Battle Mountain the Antler sequence lies unconformably on both the Harmony Formation, which is the Dutch Flat terrane (DF), and the Valmy Formation of Basin assemblage unit DCs. At Edna Mountain near Golconda and in the Osgood Mountains it lies unconformably on Cambrian and Late Proterozoic quartzite (CZq) and Cambrian phyllite and shale (Ctd) of the Nolan belt, as well as on units of the Basin and Slope assemblages (DCs, DOts). In the Cortez Mountains of northern Eureka County, it lies unconformably on Basin and Slope assemblage rocks (DCs, DOts). In the Adobe Range and the Sulphur Spring Range, it lies unconformably on Pennsylvanian and Mississippian Foreland basin rocks (IPMcl) (Trexler, Cashman, and others, 2004). In northern Elko County in the Bull Run and Copper Mountains, it lies unconformably on strongly deformed Ordovician to Cambrian rocks of the Nolan belt (OCtd). In the Snake Mountains and the HD Range, the Pennsylvanian Quilici Formation lies unconformably on the Basin and Slope assemblages (DCs, DOts, Ss) and is unconformably overlain by the Permian Siliciclastic overlap assemblage rocks (Pacl). In far northeastern Nevada, upper Paleozoic rocks around Contact are very poorly known, but are similar to the Siliciclastic overlap assemblage rocks recognized in the HD range, and are thus included in this group.

Unit consists of marine deposits of siltstone, sandstone, claystone, mudstone, limestone, and conglomerate (Stewart and Carlson, 1978). It includes rocks assigned to the Moenkopi and Thaynes Formations and related unnamed rocks in northern Nevada (Stewart, 1980). It crops out in the eastern part of the State in Elko, White Pine, Lincoln, and Clark Counties.

(Lower Mississippian and Upper Devonian)at surface, covers 0.6 % of this area

Unit crops out across all of eastern Nevada, generally east of 116 west longitude. It includes rocks mapped primarily as Pilot Shale, Joana Limestone, Chainman Shale, and their equivalents. This also includes the Tripon Pass Limestone in Elko County, the Cockalorum Wash Formation (now abandoned) in northern Nye County, the Mercury and Bristol Pass Limestones in Lincoln County, and some of the rocks mapped as Monte Cristo Limestone in Clark County. While it may be desirable to separate out the different lithologies, they are not well enough differentiated at this regional map scale. The Chainman, Joana and Pilot are grouped in White Pine County, and the Joana and Pilot are grouped in Elko County. The Pilot Shale lies depositionally (both conformably and disconformably) on Upper Devonian carbonate rocks (Dc) and signals a major change in the depositional setting across most of the carbonate platform which has long been attributed to the onset of deformation attributed to the Antler orogeny. The Pilot Shale is generally recognized as carbonaceous shale, overlain by the cliff-forming Joana Limestone. Siliciclastic quartz-bearing grit, chert, quartz sand, and siltstone in a calcareous matrix become increasingly common as the section turns into the Chainman Shale and other equivalent siliciclastic rocks. The sequence is interrupted by disconformities in a number of places, but structural disruption and poor age control hinder determination of the nature of the contacts between the distinct lithologies. Unit MDcl is overlain by unit IPMcl, but there are places where the age and distinction between the units is poorly constrained. In southernmost Nevada, in Clark and southeastern White Pine Counties, Devonian carbonate is overlain by Mississippian carbonate (Mc) with little or no intervening Pilot Shale equivalent and few overlying siliciclastic rocks with western-derived source material. North and west of the area of exposure of unit MDcl, fault-bounded slivers of Lower Mississippian and Upper Devonian platform margin and slope facies rocks with siliciclastic horizons have been grouped into unit MDst and separated from unit MDcl.

(Pennsylvanian and Upper Mississippian)at surface, covers 0.5 % of this area

Mostly Lower Pennsylvanian limestone is present in Nye, Elko, Eureka, White Pine, Lincoln, and Clark Counties, and is most commonly referred to as the Ely Limestone. A ledgy gray limestone mapped as the Moleen Formation is included here. It is not mapped separately from unit PIPc in most of White Pine County, southeastern Elko County, southern Lincoln, and western Clark Counties. Throughout most of the area of exposure unit lies conformably or disconformably beneath unit PIPc and depositionally above unit IPMcl. In southern Nye County this unit includes the Tippipah Limestone, and in Clark County it includes the Callville Limestone. In a north-south trending belt starting at the north end of the Pancake Range in Nye County and continuing north up through the Diamond Mountains along the Eureka-White Pine County border, Lower Pennsylvanian limestone is overlain unconformably by clastic rocks of the Siliciclastic overlap assemblage (Pacl, PIPacl). North of the Diamond Mountains, where Lower Pennsylvanian carbonate is not recognized separately, the coeval facies are grouped with unit IPMcl. Unit IPMbc is primarily Pennsylvanian, but in places contains Late Mississippian fossils as well.

Rocks included in this unit have been mapped as the Broad Canyon Formation and Crane Canyon sequence in Lander County (Means, 1962), the Palmetto Formation in Esmeralda and Nye Counties (Ferguson and Cathcart, 1954), the Van Duzer Limestone in northern Elko County (Coats, 1971; Coats, Howard, and Greene, 1984; Decker, 1962; Ehman, 1985), and many other unnamed and locally named rocks. These rocks are strongly deformed, although the nature of the deformation is variable across the belt (Oldow, 1984b) and not well understood regionally. This unit is usually shown both in fault contact with adjacent units Ctd and CZq and gradational with them. Unit Pacl of the Siliciclastic overlap assemblage is shown unconformably deposited on this unit in Wall Canyon of the Toiyabe Range in Nye County. In a few cases, this unit is a stratigraphic continuation from Ctd, but in most places it represents undifferentiated rocks of both Ordovician and Cambrian age that overlap with Ctd, or whose age is poorly constrained.

(Lower Cambrian and latest Proterozoic)at surface, covers 0.4 % of this area

This highly metamorphosed equivalent of CZq crops out in the Ruby Mountains and East Humboldt Range in Elko County, in the Toquima and Monitor Ranges in northern Nye County, and at the northern tip of the White Mountains in Mineral and Esmeralda Counties. In the Ruby Mountains it is transitional into OCcm, and in the White Mountains it is transitional into OCtd.

Basalt flows, plugs and dikes, some olivine basalt, and andesite and latitic rocks. This unit corresponds with unit Tb on the 1978 State map. It is present on the Washoe North, Washoe South, Lincoln, Clark, Elko, Eureka, Humboldt, Nye South, and Lander County maps.

Unit is mapped in Elko, Mineral, Humboldt, Lander, Eureka, White Pine, northern Nye, and Esmeralda Counties. Included in this unit are the Carbon Ridge Formation in Eureka and White Pine Counties, parts of the Carlin sequence of Coats (1987), the sandstone and siltstone of Horse Mountain in Elko County, the Edna Mountain Formation in Humboldt and Elko Counties, the Garden Valley Formation in Eureka County, and the Diablo Formation in northern Nye, Mineral, and Esmeralda Counties. In the Candelaria area south of Mina, unit Pacl rests unconformably on deformed Upper Cambrian through Devonian Basin assemblage (DCs) and is overlain by the Lower Triassic Candelaria Formation (TRcl). In the Toiyabe Range, it lies unconformably on deformed Cambrian through Ordovician rocks of the Nolan belt (OCtd). In the Simpson Park Mountains and the Sulphur Spring Range, it rests unconformably on Ordovician and Devonian Slope assemblage rocks (DOts). In the Diamond Mountains it rests unconformably on the Ely Limestone (IPMbc). In the Eureka area, Pacl unconformably overlies the Ely Limestone (IPMbc) and the Diamond Peak Formation (IPMcl) and is unconformably overlain by Cretaceous conglomerate (Kcg). Near Golconda it unconformably overlies PIPacl. In the Adobe Range in Elko County it overlies Foreland basin assemblage rocks (IPMcl, MDcl) and PIPacl, and in the Snake Mountains and HD Range of northeast Nevada it lies unconformably on lower Paleozoic Slope and Basin assemblage rocks (DCs, Ss, DOts) and on older Siliciclastic overlap assemblage rocks (PIPacl).

(Lower Mississippian and Devonian)at surface, covers 0.3 % of this area

Carbonaceous shale, black chert and argillite, graywacke, chert-pebble conglomerate, and detrital limestone are the primary lithologies described from all of the rocks assigned to this unit, representing a mixed slope and basinal facies. On other maps these rocks have been included in a variety of units including the foreland basin and Devonian siliceous and transitional rocks. Mapping and new biostratigraphic data gathered in the last 30 years have shown that many of these rocks mapped only as Devonian also contain Early Mississippian fossils, thus making it difficult to distinguish them from known lithologically similar Lower Mississippian rocks. Although this unit is everywhere structurally bounded by faults, a stratigraphic link to older Slope assemblage rocks is possible. These rocks are imbricated with units DCs, IPMcl, OCc, Ocq, DSt, Dc, and MDcl. Whether there is a definable continuous Early Mississippian through Devonian sequence within this unit is unknown, but is suggested in the Carlin-Piñon Range (Smith and Ketner, 1978). The Slaven Chert first described in the Shoshone Range (Gilluly and Gates, 1965) is black chert with carbonaceous shale beds 4–10 feet thick, limy brown-weathering sandstone as much as four ft thick with coarse fragments of chert, shale, greenstone, limestone, graywacke, feldspathic siltstone, and brown-weathering limestone 2–20 ft thick, and contains Late Devonian radiolarians (Boundy-Sanders, Sandberg, and others, 1999). The Mississippian Waterpipe Canyon Formation is a similar formation with basal medium-grained graywacke with interlayered black, carbonaceous shale; chert-pebble conglomerate; and bedded chert grading upward into sandstone layers with black, well-rounded quartz and a black, pyritic, phosphate- and barite-bearing, argillaceous matrix interlayered with black, platy, quartz siltstone and fine-grained graywacke interbeds. It contains Early Mississippian radiolarians (Peters, Armstrong, and others, 2003). In the HD Range in northeastern Elko County, an undated, light-gray weathering, brittle, black shale, structurally underlies the other thrust sheets and was referred to as the Chainman Shale by Riva (1970), but is included here in unit MDst. In the Windermere Hills a fissile black argillite with sporadic interbeds of quartz-chert arenite is poorly exposed with variable dips suggesting a complex structure (Oversby, 1972). In the Cockalorum Wash quadrangle along the Eureka-Nye County boundary, a pale yellow-brown, organic-detrital limestone contains quartz and chert grains locally interbedded with and succeeded upward by light-colored siliceous mudstone, claystone, and siltstone. The basal limestone contains mixed Mississippian and Devonian faunas; a thin chert from a higher zone has Osagean radiolarians (Hose, 1983). In the northern Adobe Range, this unit is recognized as dark siliceous rocks consisting of shale, argillite, and bedded chert. They are faulted and folded with sparse collections of Kinderhookian and Famennian radiolarians and conodonts (Ketner and Ross, 1990). The Webb Formation in the Carlin-Piñon Range is a gray siliceous mudstone with black to gray, tan-weathering, dense limestone in lenses near the top (Smith and Ketner, 1978). The argillite of Lee Canyon is a black siliceous argillite with a little black chert and very little conglomerate and sandstone near the top (Smith and Ketner, 1978). In the Sulphur Spring Range, the Bruffey sequence (Carlisle and Nelson, 1990) is a black chert pebble to boulder conglomerate and well-bedded gritty limestone, chert and limestone conglomerate, gray limy shale, and minor sandstone. Smith and Ketner (1978) describe the same rocks as gray limestone, sandy limestone, chert, and chert-pebble conglomerate. The Woodruff Formation from the same area is described by Carlisle and Nelson (1990) as a gray fissile shale, dolomitic siltstone, and black and brown bedded chert. Smith and Ketner (1978) describe the Woodruff as dark gray to black siliceous mudstone and chert, with lesser amounts of shale, siltstone, dolomitic siltstone, dolomite, and limestone. In the Shoshone Range, pale-red to pale-brown weathering, platy, silty dolomite interbedded with black chert in the basal 50 ft of rocks referred to as the Pilot Shale by both Gilluly and Gates (1965) and Wrucke (1974) is included here. In the southern Independence Range, this unit consists of fine-grained limestone, bedded chert, shale, conglomerate, and prominent ledges of limy sandstone with Famennian and Frasnian (Late Devonian) conodonts (Ketner, 1998). In Welches Canyon northwest of Carlin, this unit is gray to black limestone, fine grained, and thin to thick bedded with common sand- and silt-size clasts of quartz and chert grains. It also contains pebbles and cobbles of chert, and interlayered chert and siliceous shale as much as 50 feet thick (Evans, 1974). In the Snake Mountains, the unit is dark carbonaceous limestone apparently overlain by a light-gray, siliceous platy siltstone. Other outcrops that belong with unit MDst, but are not mapped separately on a regional scale from Slope or Basin assemblage units DCs and DOts include the Pinecone sequence in the Toquima Range (Coles and Snyder, 1985), and gold-bearing chert (Theodore, T., oral commun., 2006) mapped informally as the “Rodeo Creek Formation” (Peters, 1997b) in the Carlin area.

Includes some rocks mapped as the Kate Peak and Alta Formations on the Washoe South map; Wahmonie and Salyer Formations on the Nye South map; Gilbert Andesite on the Esmeralda map; pyroxene, hornblende phenoandesite, and phenodacite on the Elko map; and other unnamed units. It corresponds to the unit Ta3 on the 1978 State map. It is present everywhere except Eureka and White Pine Counties.

Tertiary felsic intrusive rocks are widely scattered in every county across the State. They are generally described as granitic rocks, granodiorite, monzonite, quartz monzonite, alaskitic granite, quartz diorite, dacite, and rhyodacite in the places where they are shown separately on county maps.

Crops out over the same area as unit Dc. Its primary formations are the Sevy Dolomite and the Nevada Formation (now abandoned). In White Pine County, there may be some undivided Guilmette Formation included with unit Dcd. Also included are the Lower Devonian Tor and McMonnigal Limestones in northern Nye County. The Simonson Dolomite is also included here as it is not differentiated in White Pine and Elko Counties. These rocks correspond to depositional sequences 6, 7, and 8 of Cook and Corboy (2004). Unit Dcd is overlain by unit Dc and is depositional on DSc. In White Pine County and most of Elko County, unit DSc is not broken out from unit SOc, hence the Devonian dolomite sequence appears to rest directly on SOc.

(Lower Cambrian and latest Proterozoic)at surface, covers 0.3 % of this area

These lowermost Cambrian to Precambrian strata are scattered over much of central and eastern Nevada and form the base of the Phanerozoic part of the continental margin stratigraphic section. They include the Campito, Deep Spring, Harkless, and Poleta Formations, and the Reed Dolomite in Esmeralda County; the Gold Hill Formation in northern Nye County; unnamed quartzite and shale in White Pine County; the Osgood Mountain quartzite in Humboldt County; the Prospect Mountain Quartzite in northern Nye, Lincoln, Eureka, and Elko Counties; unnamed quartzite and shale in Lander and Clark counties; and the Stirling Quartzite, Wood Canyon Formation, and Zabriskie Quartzite in southern Nye County. In a number of places, these rocks are depositional on Late Proterozoic unit Zqs. In southernmost Clark County, CZq is lying unconformably directly on Early Proterozoic gneiss (Xm). In the east-central part of Nevada, CZq is overlain depositionally by Cambrian carbonate (Cc) of the Carbonate shelf sequence. In the Nolan belt, these rocks are depositionally overlain by unit Ctd. In the Osgood Mountains in Humboldt County, Permian and Pennsylvanian rocks of the Siliciclastic overlap assemblage (PIPacl, Pacl) rest unconformably directly on the Osgood Mountain Quartzite.

Occurs in southern and eastern Nevada. The Bonanza King and Carrara Formations are the primary formations in southern Nye County; the Dunderberg Shale in northern Nye and Lincoln Counties; the Hamburg Dolomite in Eureka County; the Nopah Formation in southern Nye and Esmeralda Counties; the Patterson Pass and Pioche Shales, the Chisholm and Highland Peak Formations, and the Lyndon Limestone in Lincoln County; the Pole Canyon Limestone and the Lincoln Peak and Windfall Formations in northern Nye County; and undifferentiated limestone and dolomite in Lincoln, Clark, White Pine, Eureka, northern Nye, and Elko Counties. This unit is conformably overlain by the Ordovician shelf rocks (OCc), and is depositional on the underlying Proterozoic-Cambrian quartzite of CZq.

(Lower Silurian to Middle Ordovician)at surface, covers 0.3 % of this area

Ely Springs Dolomite and Hanson Creek Formation are the main formations included in this unit. Many of the rocks in this unit are not assigned to a formation. A large section of the carbonate platform from Early Devonian through latest Ordovician time is represented by dolomitic rocks. They commonly look similar, have poor biostratigraphic control, and thus are not always well differentiated on the county maps. Additionally, not all of the dolomite is primary, and thus boundaries between secondary dolomite and other rock units have been misinterpreted as primary stratigraphic boundaries, further confusing the stratigraphy of the lower Paleozoic shelf (Nichols and Silberling, 1977a). Rocks in this unit correspond to sequence 4 of Cook and Corboy (2004). This unit includes rocks deposited immediately above the Eureka Quartzite, but disconformably below the Lone Mountain and Laketown Dolomites, hence it includes the Silurian and uppermost Ordovician. Rocks included in unit SOc that are mapped as the Hanson Creek Formation are depositionally overlain by the Roberts Mountains Formation of unit DSt in the northern and western part of the exposure area. The SOc rocks mapped as Hanson Creek Formation are difficult to distinguish from units DSt and DOts, and should more appropriately be included in unit DOts, but inconsistent mapping makes this difficult. In general unit SOc is not differentiated from unit OCc in Clark County, and thus unit DSc lies directly on unit OCc. In Lincoln and Nye Counties unit SOc lies directly on the Eureka Quartzite (Ocq) and is overlain by the Laketown Dolomite (DSc). In southern Nye County, rocks mapped as Ely Springs Formation are grouped with the Eureka Quartzite as unit Ocq. In White Pine and eastern Elko Counties, the Eureka Quartzite is not mapped separately, and unit SOc therefore lies directly on unit OCc, which includes the quartzite. Also in White Pine and eastern Elko Counties, unit DSc is not differentiated from unit SOc, so SOc is overlain directly by unit Dcd. In the northern and western areas of exposure where unit SOc is mapped as Hanson Creek Formation it is overlain depositionally by unit DSt of the Slope assemblage.

Platy limestone, dolomite and chert are characteristic of the auriferous Roberts Mountains Formation in Nye, Elko, Eureka, and Lander Counties and of the Masket Shale and Gatecliff Formation in northern Nye County. This unit lies with depositional contact over the Hanson Creek Formation of unit SOc of the Carbonate shelf sequence (unit OCc in southern Nevada), and is also structurally imbricated with Carbonate shelf sequence rocks (OCc) and other Slope and Basin assemblages rocks (units DCs, DOts, MDst) across its area of exposure. In the Carlin area, rocks assigned to the Popovich Formation and the informal Bootstrap Limestone (Berger and Theodore, 2005; Jory, 2002) are also included. In the Monitor Range, the Roberts Mountains, and the Sulphur Spring Range, unit DSt is mapped as stratigraphically overlain by unit DSc. To what extent this “overlying” dolomite is truly a stratigraphic unit as opposed to an alteration product of this unit (Nichols and Silberling, 1977a) is unclear. A stratigraphic contact with unit MDst in the Carlin area is possible based on recent mapping (Berger and Theodore, 2005; Theodore, Moring, and others, 2003).

Locally includes minor amounts of tuff. It includes rocks mapped as the Titus Canyon Formation on the Nye South map, the Gilmore Gulch Formation on the Nye North map, lacustrine limestone in Lincoln County, and other unnamed units. This unit corresponds to unit Ts2 on the 1978 State map. It is present in Nye, Lincoln, Elko, and Lander Counties.

Generally poorly age constrained. This unit includes rocks originally mapped as the Pyramid sequence in Washoe County, the Mizpah Trachyte in Nye County, the Malpais Basalt, Rabbit Spring Formation, and Mira Basalt in Esmeralda County, and many other poorly dated unnamed basaltic and andesitic rocks around the State. It corresponds to unit Tba on the 1978 State map.

Because of its importance as a stratigraphic marker horizon, the Eureka Quartzite is depicted on this map wherever it is mapped separately from the Ordovician carbonate shelf rocks. It represents depositional sequence 3 of Cook and Corboy (2004). It is not differentiated from the rest of the Ordovician (OCc) in White Pine or Clark Counties, but is shown in Elko, Eureka, Nye, and Lincoln Counties. Rocks mapped as the Ely Springs Dolomite are included with the Eureka Quartzite in southern Nye County. The Eureka Quartzite depositionally overlies the Pogonip Group (OCc), and is overlain by either the Hanson Creek Formation or the Ely Springs Dolomite (SOc).

Limestone, quartzite, dolomite, siltstone, conglomerate, and metamorphic rocks crop out in the southeastern, east-central, and northeastern regions of the State as part of Zqs. It forms the Proterozoic base of the continental margin stratigraphic section. This unit includes the Johnnie Formation in southern Nye and Lincoln Counties, schist in Elko County, the McCoy Creek Group metamorphic rocks in Elko and White Pine Counties, and the Wyman Formation in Esmeralda and southern Nye Counties. This rock is overlain by CZq. Its base is not exposed.

Limestone, basalt, chert, and volcaniclastic rocks. The Home Ranch subterrane of the Golconda terrane shares similar structural characteristics with the rest of the Golconda terrane, but it has more specific age and lithologic features. It is restricted to Mississippian age (generally Early) and consists of shallow-water fossiliferous limestone, black chert, basalt, and volcaniclastic rocks. Olistostromal debris flows of basalt and limestone, indicative of steep paleotopography, are a distinguishing characteristic (Jones, 1991a). The depositional setting for this subterrane can be interpreted as a seamount. It includes rocks in Elko County mapped as the Banner and Nelson Formations, at least parts of the Inskip Formation in the East Range in Pershing County, the Goughs Canyon Formation in the Osgood Mountains, similar rocks in the Hot Springs Range in Humboldt County, and likely includes Mississippian limestone in the San Antonio Mountains in northern Nye County. To what extent these rocks have a history distinct from other rocks of the Golconda terrane is unclear. They are present structurally in a position outboard or west of most other exposures of the Golconda terrane, and are separated in the northern part of the State from other exposures of the terrane by the Nolan belt.

Unit corresponds with sequence 5 of Cook and Corboy (2004) and includes the Laketown and Lone Mountain Dolomites and equivalent unnamed rocks. In White Pine County these rocks are grouped with the underlying unit SOc, but otherwise are mapped in Elko, Eureka, Nye, Lincoln, and Clark Counties. Disconformities and discontinuities are commonplace along both upper and lower contacts (Langenheim and Larson, 1973). Unit DSc is depositionally overlain by unit Dcd, except where those rocks are grouped with unit Dc. In general, unit DSc overlies unit SOc. In Clark County and parts of Elko County, unit SOc is not differentiated from unit OCc, and therefore DSc lies directly on OCc. In the Sulphur Spring Range, DSc depositionally overlies unit DSt, and in the Roberts Mountains it grades laterally and vertically down into unit DSt. The Lone Mountain Dolomite has been shown to be both primary and secondary dolomite (Nichols and Silberling, 1977a). Therefore the boundaries mapped between unit DSc and both underlying DSt and overlying Dcd are not primary depositional features in all cases, especially in the Roberts Mountains.

Shale, thin-bedded limestone, phyllite, hornfels, quartzite, chert, and siltstone are typical of this Cambrian unit which exhibits regional metamorphism suggesting significant burial depths have heated and recrystallized many of these rocks. This unit includes rocks mapped informally as the Bull Run Dolomite and Edgemont Formation in northern Elko County by Ehman (1985); the Crane Canyon sequence in the Toiyabe Range; some regions mapped as Dunderberg Shale; and the Swarbrick Formation in northern Nye County, the Emigrant Formation in southern Nye and Esmeralda Counties, the Mule Spring Limestone in Esmeralda County, the Preble Formation in Humboldt and Pershing Counties (Madden-McGuire, 1991), the Paradise Valley Chert in Humboldt County, and the Schwin Formation (Gilluly and Gates, 1965) in the Shoshone Range in Lander County. In most exposures this unit lies transitionally above the Cambrian-Precambrian quartzite unit CZq. In places this unit is transitional into OCtd. This unit is also in structural contact with DCs, DOts, OCc, OCtd, CZq, the Golconda terrane (GC), and the Dutch Flat terrane (DF). In the Osgood Mountains (Boskie and Schweickert, 2001; Crafford and Grauch, 2002; Madden-McGuire and Marsh, 1991), the Bull Run Mountains (Ehman, 1985), the Toiyabe Range (Means, 1962), and the Miller Mountain area (Oldow, 1984b) these rocks exhibit complex polyphase deformation with a strong west-vergent component. At Edna Mountain near Golconda in Humboldt County, these rocks are unconformably overlain by both Pacl and PIPacl of the Siliciclastic overlap assemblage.

In the HD Range in northeastern Elko County, the Noh Formation was described by Riva (1970) and consists of a basal, dark-gray chert and light-gray shale, light-brown weathering, siliceous and tuffaceous siltstone and shale, and tan- and light-brown-weathering, thin-bedded siltstone, sandstone, and minor shale. It contains a large and diagnostic Wenlockian (Early Silurian) graptolite fauna, and is partly coeval with the base of the Roberts Mountains Formation (DSt) which also has a conspicuous basal chert ledge. The similar age Elder Sandstone in Lander and Eureka Counties was named for moderately cemented sandstones exposed in the Shoshone Range (Gilluly and Gates, 1965). It is primarily a fine-grained, silty sandstone, sandy siliceous and tuffaceous shale, and thin, platy, light brown chert. Much of the sandstone and siltstone is notably feldspathic, including abundant angular fragments of potassium feldspar, and has reportedly interbedded rhyolite in places (Theodore, T., oral commun., 2006). It is grouped with unit DCs or DOts in many places. Its unusual lithologic characteristics warrant a separate grouping where it can be separated from these units (Noble, Finney, and Cluer, 2000). Zircon studies have suggested that the feldspathic source material for these rocks was not located adjacent to the Nevada part of the continental margin, but is derived from a source either farther to the north or in Mexico (Gehrels, Dickinson, and others, 2000). Likewise, tuffaceous source material for the shale described in the Noh Formation is not known from the Nevada continental margin of this time. Like most other rocks of the Slope and Basin assemblages, unit Ss is everywhere in structural contact with other Paleozoic rocks. It is structurally imbricated with units DCs, DOts, and MDst. Whether these rocks have traveled a significant distance either toward or along the margin as discrete tectonic blocks or as sediment transported in offshore turbidity systems is not known, but no basement is preserved with them, and they are unconformably overlain by the Pennsylvanian and younger Siliciclastic overlap assemblage.

The metamorphosed Eureka Quartzite is shown separately in the Ruby Mountains, East Humboldt Range, and Wood Hills in Elko County, and serves as a valuable marker horizon for the thick sequence of metamorphosed lower Paleozoic shelf rocks.

Includes rocks mapped as the rhyolite of Big Sand Springs Valley on the Nye North map, the Sandstorm Formation in Esmeralda County, rhyolite flow domes in the Sheep Creek Range in Lander County, and other units. It corresponds to unit Tr2 on the 1978 State map. It is present in Nye, Lincoln, Churchill, Esmeralda, Eureka, Mineral, Elko, Humboldt, and Lander Counties.

Breccias of various origins are scattered across Clark, Nye, Lincoln, Elko, Eureka, Lander, and White Pine Counties. Most are interpreted to be Tertiary in age, but have tectonic, volcanic, and metamorphic origins, and include jasperoids, brecciated tuffs, exotic slide blocks, landslide deposits, megabreccia, thrust breccia, and debris beds.

(Lower Jurassic and Upper Triassic)at surface, covers < 0.1 % of this area

These continental deposits include variegated bentonitic claystone, siltstone, and clayey sandstone, ledge-forming sandstone, and red siltstone (Stewart and Carlson, 1978). The lower part of this unit is equivalent to the Upper Triassic Chinle Formation and the upper part corresponds to the Moenave and Kayenta Formations which are now considered Lower Jurassic (Stewart, 1980). It crops out in Elko, Lincoln, and Clark Counties.

Flows and cinder cones of olivine tholeiite basalt, and shallow basalt intrusives (~15-3 Ma); includes basalt in Owyhee County and southwest of Twin Falls, basalt of Weiser (basalt to andesite), basalt of Cuddy Mountain (alkali basalt and picro-basalt) north of Cambridge, basalt in Mount Bennett Hills north of Gooding, andesite at Square Mountain near Magic Reservoir, and Cub River diabase sill east of Preston. Includes gabbro at depth in cross section D-D’-D”. (Quaternary to Eocene Continental Volcanic and Intrusive Rocks).

Tertiary rhyolitic intrusive rocks also are present in every county of Nevada. They include many rocks mapped as rhyolite or rhyolite porphyry, rhyolite intrusive rocks, rhyolite plugs or flows, microgranite dikes, and many other undifferentiated intrusive rocks.

Includes detrital deposits of continental origin, and locally derived fluvial and lacustrine clastic rocks, some interbedded with siltstone and freshwater limestone. Outcrops are concentrated in three separate areas of the State. In each place, limited biostratigraphic data indicate these rocks are Cretaceous. The King Lear Formation in the Jackson Mountains in Humboldt County lies unconformably on Triassic and older rocks of the Black Rock-Jackson terrane. The Newark Canyon Formation crops out mostly in Eureka and White Pine Counties but extends into Elko and Nye Counties as well, and rests unconformably on Ordovician to Permian rocks. In places it is difficult to distinguish Upper Devonian, Pennsylvanian, and Permian clastic rocks also derived from the nearby underlying bedrock from the Newark Canyon Formation, and some confusion still exists. The Willow Tank Formation in Clark County lies unconformably on Jurassic rocks and is overlain by what was mapped as the Baseline Sandstone and Overton Fanglomerate (now referred to as the Overton Conglomerate Member of the Baseline Sandstone), all of Cretaceous age.

(Middle Miocene to Late Pliocene)at surface, covers < 0.1 % of this area

Salt Lake Formation and other Basin & Range valley-filling alluvial, lacustrine, and volcanic materials. Valley fill is more than 8,000 feet thick in places and includes salt masses under the Sevier Desert.

Marine phosphorite, shale, and chert of Phosphoria Formation, fine-grained sandstone and mudrock of Wells, Quadrant, Amsden, and Shedhorn formations, and fine-grained sandstone, carbonaceous mudstone, and limestone of the Snaky Canyon Formation and Sun Valley and Oquirrh groups. Located in south-central and eastern Idaho. (Paleocene to Neoproterozoic Sedimentary and Igneous Rocks of the Cordilleran System).